I found this on Vinted, it's for the Atari 2600, and from what I can find out there was only one game released that took advantage of it, Star Raiders, which was included with the controller
You get twelve buttons in a rectangle shaped handheld
It has rubber feet and plugs into the normal controller port
Game specific overlays could be used
The Star Raiders game with instructions and keypad overlay
P - FN without DEF, 870:1